It is often necessary to install a pitot tube type of fluid flow meter into a conduit while pressurized liquid or gas is flowing in the conduit. Apparatus has been designed to implement this type of installation, including, for example, the Rosemont 485 Annubar® Flanged Flo-Tap Assembly. In making use of this or similar apparatus to insert a sensor into a pressurized fluid conducting conduit it is extremely difficult to determine whether the bluff body sensor portion of the averaging pitot tube is completely inserted in the conduit, that is, inserted diametrically into the conduit so that the distal end of the bluff body sensor is in firm and stable contact with the inside surface of the conduit opposite the point of insertion. If not firmly seated against the wall of the conduit the sensor is subject to breaking. Conversely, the pitot tube sensor can be damaged if the insert-retract mechanism is over tightened during installation. One particular technique of the prior art utilizes colored markings on the sensor to visually indicate the distal end's approach to the far side of the conduit. Such a method however, lacks the finesse necessary to insure proper seating of the sensor or guard against damage during insertion. Furthermore, during actual operation of the flow meter, if the signal from an averaging pitot tube disappears it is very difficult to determine whether the bluff body has broken away from the pitot tube assembly or whether its pressure ports are plugged. Additionally, with the current state of the art there is no way to verify whether an averaging pitot tube is accurately tracking the changes in the fluid flow rate in a conduit.
Accordingly, the primary object of the present invention is to establish a method and apparatus that will overcome the aforesaid difficulties encountered in the installation and proper monitoring of the operation of an averaging pitot tube type of fluid flow meter.
A further object of the invention is to create, with the same apparatus as employed for detecting the proper seating of the pitot tube bluff body on the opposite conduit wall, redundant measurement of fluid flow rate by use of the Von Karman effect.